Principal research efforts during the past year were on filariasis, leishmaniasis, and toxoplasmosis. Specificity of the IgE response in patients with tropical eosinophilia has been tested in a system of passive sensitization of human basophils to determine whether a specific antigen producing histamine release can be identified. An expedition to the Cook Islands of the Pacific was organized for studies of filariasis, with primary emphasis on immunologic responsiveness of patients with this infection. Patients with leishmaniasis and toxoplasmosis were utilized for tests of cell mediated immunity and for circulating antigen, respectively.